Percutaneous transluminal coronary angioplasty (PTCA) is a common procedure for treating heart disease. A problem associated with PTCA includes the formation of intimal flaps or torn arterial linings which can collapse and occlude the conduit after the balloon is deflated. Moreover, thrombosis and restenosis of the artery may develop over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. To reduce the partial or total occlusion of the artery by the collapse of arterial lining, and to reduce the chance of the development of thrombosis and restenosis, a stent may be implanted in the lumen to maintain the vascular patency.
Stents are generally tubular-shaped devices which function to hold open or reinforce a segment of a blood vessel or other body lumen, such as a coronary artery, carotid artery, saphenous vein graft, or femoral artery. They also are suitable to support and hold back a dissected arterial lining that could occlude the body lumen, to stabilize plaque, or to support bioprosthetic valves. Stents are typically delivered to a target area within the body lumen using a catheter. A balloon-expandable stent is mounted to a balloon catheter, navigated to the appropriate area, and expanded by inflating the balloon. A self-expanding stent is delivered to the target area and released, expanding to the required diameter to treat the disease.
Stents are used not only as a mechanical intervention but also as a vehicle for providing biological or pharmaceutical therapy. As a mechanical intervention, stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Biological or pharmaceutical therapy can be achieved by medicating the stents, in particular by using drug-eluting stents, DESs. DESs can provide local administration of a therapeutic substance, such as a drug, a pharmaceutical agent, or a biologic at the specific site in a patient's body. This can result in fewer and less severe side effects and more favorable overall results.
Implantable medical devices such as stents can be formed from various materials, such as polymeric and/or metallic materials, and may be non-degradable or biodegradable. An implantable device can be fabricated with a coating containing partially or completely a biodegradable polymer, a biostable polymer, or a combination thereof. An implantable device body can be fabricated partially or completely from a biodegradable polymer, a biostable polymer, or a combination thereof.
Biodegradable polymers may degrade by hydrolysis and other reaction mechanisms in the vascular or other luminal environments over time. Usually, it will be desirable to have the stent or endoprosthesis completely degrade after it has served its needed supporting function in the body lumen. Typically, complete degradation will be desired in less than three years, sometime less than one year, or in a matter of months after implantation.
Polylactide (PLA) based polymers have been used to fabricate bioabsorbable implantable medical devices. Although PLA based polymers have been used widely in many lactide based drug delivery systems, the present inventors have found that modification of their chemical structure can broaden their application.